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I intend to finish a part of my basement following this guideline from Fine Homebuilding and Building Science. There are two options I could come up with for installing hydronic radiant heat extrusions, and I can't decide which of the two is most ideal.

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Option 1 - Route out a pathway into the insulation that would fit the aluminum channel, then cover with the two layers of 1/2" plywood, then cover with flooring Option1

Option 2 - Start with 2" foam, put down 1/2 ply screwed into the concrete, put down aluminum channel on top of 1/2" plywood, cut strips of 3/4 plywood to go between channel, install flooring over 3/4 Option2

Option 1 is much easier to build. The foam will have some "give" when fastening the plywood against the aluminum plate, which will ensure contact and allow flatter flooring layers above. I just fear the aluminum on insulation contact, movement and directly heating the insulation. There are adhesives to secure the aluminum to the foam if that's appropriate.

Option 2 provides more "structural" support to the channel to prevent noise, as well as providing more thermal mass and more isolation from the insulation. I'm not sure if the layers of plywood will have enough "give" to encapsulate the aluminum track without causing the surface to bow.

StayOnTarget
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kavisiegel
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  • Which [type of hydronic system](https://en.wikipedia.org/wiki/Hydronics#Types_of_hydronic_system) will it be? Cooling? Heating? And what kind of temperature? – wallyk Dec 08 '16 at 02:14
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    The wood is not a good conductor of heat. Foam is horrible. I would recommend you bed your pipes in something that conducts heat. – Damon Dec 11 '16 at 09:29
  • @Damon that's what the aluminum extrusion is for :) – kavisiegel Dec 12 '16 at 14:45
  • @kavisiegel Putting the aluminum extrusions on the pipes is not "bedding them in aluminum". I think the aluminum is suppose to help increase the heat transfer from the small plastic tubing to the radiant floor substrate; then the substrate radiates to the room. In your case, the substrate your radiant floor is foam (an insulator) and wood of which neither are comparatively good conductors of heat. I again say the same; I would recommend you bed your pipes in something that conducts heat better than foam and wood. You don't have to though! :) – Damon Dec 12 '16 at 15:58
  • Cutting plywood will be much easier and less messy than routing rigid insulation. I'd go with #2. – StayOnTarget Mar 13 '18 at 00:38
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    There is also a variant of #2 where the radiant panels are "face up" so much more of the metal surface area is in direct contact with the flooring above. – StayOnTarget Mar 13 '18 at 00:39
  • What is the point of screwing the plywood to the concrete? That will introduce a massive cold bridge, for no particular benefit. (My basement floor is 25mm OSB floating on wood fibre - with a vapour barrier over the fibre.) – Martin Bonner supports Monica Nov 18 '19 at 10:16
  • @MartinBonnersupportsMonica Concrete floors aren't perfectly flat, unless you put a lot of effort in to ensure that. If you don't screw it down, it _could_ have spring to it depending on how thick the plywood and the size of the peaks and valleys of the concrete. If you knock down the peaks and do 2 layers of 3/4 plywood screwed together, I think that's safe to float without securing to the concrete. That being said, interesting thought on the screws being thermal bridges. You'd want the screws not touching the aluminum fins for sure. – kavisiegel Nov 24 '19 at 16:26
  • @kavisiegel Ah. The wood fibre insulation will have eliminated any lack of level in the concrete underneath my floor. – Martin Bonner supports Monica Nov 24 '19 at 16:29
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    I’m voting to close this question because it's been abandoned – FreeMan Dec 13 '20 at 20:22

1 Answers1

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For a ThermoFin U extruded aluminum heat transfer plate installation on concrete, you would build a surface to be able to screw the plates into by first putting down a layer of Atlas Rboard®, recommended 1/2", which you should be able to get from your local building supplier. A Google search on Atlas Rboard® will bring up their site and the product info.

On top of the Rboard® put down a layer of plywood. The fasteners will hold best if you can use 3/8" plywood. It will work with 1/2" plywood if necessary.

Keep in mind that you want the heat energy to be going into the sleepers and the finish floor, which is why we recommend the Rboard®.

The energy without the layer of insulation will be drawn into the concrete, and the response time would be longer in heating the floor. Heating up the mass of concrete is not necessarily a good thing when you want the entire surface floor to be warmed.

Radiant Engineering aka Radiant Design & Supply has decades of success with ThermoFin U and ThermoFin C installations in North America. Install ThermoFin U with the fins facing down for wood finish flooring. For tile or stone, install with the fins facing up. The sandwich of aluminum and plywood provide an evenly heated surface that is friendly to finish flooring installation. ThermoFin U specs are .050" gauge, width 4", length either 4 ft or 8 ft, tubing channel size either nominal 1/2" or 3/8".

Dale Pickard
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    Hi Dale. To clarify, it sounds like you're more on the side of option 2 as posted above if using hardwood or carpet, but more in favor of an "option 3" for tile, where everything is similar to option 2 except the aluminum channel is on top of the 3/4 ply rather than below it? – kavisiegel Mar 13 '17 at 16:03
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    If you are affiliated **in any way** with the product that you linked to, you **must** disclose that. Please see the [expected behavior](/help/behavior), [product support](/help/product-support) and [promotion](/help/promotion) pages in the [help] for more information. – Niall C. Mar 14 '17 at 17:23
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    @NiallC. Reads like an advertisement or "product support page". Still could be useful information, but need to know the real source. – manassehkatz-Moving 2 Codidact May 22 '18 at 18:58